Abstract:
A method for performing rate 2/3 Multiple Amplitude Shift Keying (MASK) encoding utilizing a rate 1/2 convolutional encoder (10) is described. In accordance with one embodiment of the invention, a rate 1/2 encoder is used to generate two coded symbols and a second bit is used as an uncoded symbol. A mapper (20) generates amplitude modulation data in response to the uncoded symbol and the pair of coded symbols whereby the uncoded symbol is the most significant. In a decoder, a variable threshold decoder (88) is used to determine the uncoded symbol where the threshold is varied on the set of coded symbols received.
Abstract:
A novel and improved method and apparatus for providing an interface to a digital wireless telephone system compatible with standard analog wire line telephones and analog wire line fax machines are disclosed. During a telephone call, a fax detector (11) monitors the incoming data for fax signals. If a fax is detected, the data processor (12) switches from processing the data as if it were voice to processing it as fax. In addition, the remote station is sent a signal notifying it to process the data as fax rather than voice. The fax detector (11) operates by detecting the preamble of a V.21 message, present at the beginning of every fax call. Energy is measured in both frequencies of the BFSK signals. A decision is made by analyzing these energies and locating a specific pattern which repeats itself a sufficient number of times.
Abstract:
A system and method for determining the transmission rate of a data signal at a receiver of a variable rate communications system. A vocoder at a transmitter encodes a frame of data into symbols according to one of a set of discrete data rates. When the data rate is lower than the maximum, each symbol is repeated a number of times as required to achieve a constant number of symbols in each frame. The data signal is transmitted at a power proportional to the data rate of the frame. A reference signal is also transmitted. The reference signal is transmitted at a constant power. Further, the data signal has the same carrier frequency as a reference signal so that they exhibit the same fading characteristics as they are transmitted through the channel. At a receiver, the power of the reference signal is measured by the pilot measurement element (36) and the power of the data signal is measured by the traffic power measurement element (38). The rate processor (46) dtermines the ratio of the power of the data signal to the power of the reference signal, and the measured ratio is compared with a predetermined ratio of the power of a maximum rate data signal to the power of the reference signal. The result of the comparison will indicate the encoded data rate of the received frame of data. The decoder (40) then uses the rate indicated by the comparison to properly decode the frame of data. A vocoder at the receiver further processes the data for interface with the user.
Abstract:
The invention is a method and apparatus for providing an Alert With Information Message signal between a mobile switching center (36) and a base station (34) in a cellular communication system. The invention recognizes that current provisions of the IS-634 standard lack support for certain required functionality on the interface between a mobile switching center (36) and a base station (34), or the A-Interface. An Alert With Information Message signal is introduced on the A-Interface to support the required functionality. Introduction of the Alert With Information Message provides support for reliable call processing on the A-Interface for the call waiting procedure, the hard handoff procedure, and the resolution of a glare condition. A message generator (38) in the mobile switching center (36) generates the Alert With Information Message, which is transmitted to message receiver (40) in the base station (34) when needed.
Abstract:
A system and method for determining the position of a user terminal (for example, a mobile wireless telephone) in a low-Earth orbit satellite communications system (100). The system includes a user terminal (106), at least one satellite (104) with a known position and velocity, and a gateway (102) (that is, a terrestrial base station) for communicating with the user terminal (106) through the satellite (104). The method includes the steps of determining a range parameter (802) and a range-rate parameter (806). A range parameter represents a distance between the satellite and the user terminal. A range-rate parameter represents a relative radial velocity between that satellite and the user terminal. The position of the user terminal on the Earth's surface is then determined (810) based on the range parameter, the range-rate parameter, and the known position and velocity of the satellite.
Abstract:
A system and method for resolving ambiguity in an ambiguous position solution for a user terminal position in a satellite communications system which includes a user terminal (106), at least one satellite (104), and a gateway (102) communicating with the user terminal (106) through the satellite (104). Each satellite (104) has a plurality of satellite beams (601-616) which each illuminate a region on the Earth in a known pattern relative to a satellite sub-track (404). A satellite beam (601-616) illuminating the user terminal (106) is identified along with its corresponding position relative to the sub-track (404). The orientations of possible user terminal positions (408A, 408B) and the identified beam (601-616) relative to the satellite sub-track (404) are compared to each other. Possible user terminal positions (408A, 408B) falling on an incorrect side of the sub-track (404) from the detected beam (601-616) illuminating the user terminal (106), are considered as incorrect solutions for that user terminal (106). The ambiguity solution can be determined using satellite identification and comparison elements in the user terminal (106), or at the gateway (102), in which case certain beam information is reported to the gateway (102). In further aspects of the invention, the beam being identified can be either a forward link (601-616) or reverse link (621-636) beam, or both, and each link has a different beam pattern.
Abstract:
A handoff technique in which system users detect transitions in service between a current service area (B10, S4) and an adjacent service area (B2, S5), and request a forward link channel in the new service area (B2, S5) when a detected signal strength for the new service area exceeds predetermined threshold levels. The forward communications link in the current service area is maintained until the strength of the new service area signal (B2, S5) reaches a certain level and appropriate channel quality is confirmed, as based on various known criteria. Typically, service area transitions are detected using the signal strength of pilot or paging signals associated with service areas, which are used to determine a relative signal strength of new service area signals. Pilot signal level adjustments used to counter roll-off effects are detected and compensated for in comparing signal levels. To minimize the burden on system resources, new service area signals are not selectable until a minimum time has passed, or a minimum change in energy from a prior pilot signal is detected. In addition, communications using the previous service area can be dropped almost immediately upon engaging the new service area.
Abstract:
The mobile telephone detects bad data packets by decoding speech parameters represented by the packets and comparing those speech parameters against acceptable ranges of speech parameters. If the speech parameters do not lie within the acceptable ranges, the packets are discarded. This speech parameter-based detection of bad data packets is particularly useful in mobile telephones receiving variable rate data packets wherein an error in determining the rate of a packet results in the entire packet being decoded at an incorrect rate, thereby likely causing an annoying audible artifact in the decoded speech signal. Such rate detection errors can occur eventhough a CRC or other conventional error detection check fails to detect the bad packet. In an exemplary implementation, receiver (132) of mobile telephone (128) receives signals encoded with TIA/EIA/IS-95-A standards. Variable rate decoder (140) determines linear speech parameter frequencies and codebook gain parameters using linear predictive coding techniques. The parameters are tested against acceptable ranges to detect bad data packets by speech parameter examining unit (144).
Abstract:
In a communications network, a network user communicates through a remote unit (155) via at least one base station (150). The communications network includes a first mobile switching center (100) for controlling communications through a first set of base stations (102) and a second mobile switching center (112) for controlling communications through a second set of base stations (108). The network also includes a service providing base station (102D) controlled by the first mobile switching center (100) and providing service to a first transition coverage area using a first pseudorandom noise code. The first transition coverage area defines a boundary between a first system (102) controlled by the first mobile switching center (100) and a second system (108) controlled by the second mobile switching center (112). The network further includes a passage providing base station controlled (108D) by the second mobile switching center (112) for providing service to the first transition area using a second pseudorandom noise code offset in time by a first amount from the first pseudorandom noise code. The passage providing base station provides service to a remote unit (155) only if the remote unit (155) is entering the first transition coverage area while exiting the second system or is about to exit the first transition coverage area while entering the second system.
Abstract:
The finite impulse response (FIR) filter (20) is implemented as a table (104) using read-only memory (ROM). The FIR filter table stores a pre-calculated output filter value for each permissible combination of input values (102) to be filtered. Streams of input values are successively shifted into the table using a shift register (106) and corresponding output values are successively output. The telephone employs a data burst randomizer (18) to provide a data signal composed of sequences of null or 0 values and sequences of antipodal values (+1's and -1's). Hence, the permissible input combinations for the FIR filter include only patterns containing either all antipodal signals, all null signals, leading antipodal signals followed by trailing null signals, or leading null signals followed by trailing antipodal signals. The FIR filter look up is configured to exploit these limitations on the input streams yielding a look up table having relatively few entries.